An offset printing unit has a plurality of rotatable cylinders, including a plate cylinder and a blanket cylinder. The plate cylinder carries a printing plate having a surface on which an inked image is defined. The blanket cylinder carries a printing blanket. The plate on the plate cylinder transfers the inked image to the blanket on the blanket cylinder at a nip between the plate cylinder and the blanket cylinder when the cylinders rotate. The blanket on the blanket cylinder subsequently transfers the inked image to the material being printed, such as a web of paper.
A printing blanket is conventionally formed as a sheet, and is mounted on a blanket cylinder by wrapping the sheet around the blanket cylinder. A printing blanket can alternatively be formed as a tube which is mounted on a blanket cylinder by sliding the tube telescopically over the blanket cylinder. Such a tubular blanket has a cylindrical sleeve which supports the blanket in a tubular shape. The sleeve and the blanket cylinder are designed so that the sleeve is receivable over the blanket cylinder with an interference fit. The blanket cylinder is equipped with air flow passages and openings to direct a pressurized flow of air over the blanket cylinder. When the sleeve in the tubular blanket is located over the air flow openings in the blanket cylinder, the pressurized flow of air expands the sleeve diametrically. The expanded sleeve can be moved axially onto, or off of, the blanket cylinder when in its expanded condition. When the pressure is relieved, the sleeve contracts diametrically against the blanket cylinder and thus establishes an interference fit with the blanket cylinder.